**3. Traditional horticulture in the southern Green belt of Buenos Aires**

Horticulture depends on the soil; therefore the conservation of this resource is essential to ensure the development of the sector. The intensive use of the soil, based on the overuse of inputs for many years (fertilizers, pesticides, disinfectants), added to irrigation with low quality water (sodium bicarbonate) [21], has generated negative impacts associated with soil pollution and degradation. The alteration of soil physical, chemical and biological properties resulted in a fragile productive system with a high risk of environmental impact [22, 23].

Soil physical condition establishes its sustainability, root penetration, air circulation, water storage capacity, drainage, nutrient retention, among other factors. The texture (proportion clay, silt and sand) determine the amount and availability of water, nutrients, aeration and drainage. Soils with fine texture (clay more than 40% or silt more than 60%) have a high water and nutrient retention capacity. However, it must be handled with caution because they are easily compacted. Likewise, crops sensitive to soil pathogens are more susceptible in heavy textured soils. Fertirrigation has counteracted these disadvantages. Soil compaction reduces porosity and increases its bulk density. This limits the space for the storage or movement of air and water within the soil. It is the cause of a physical restriction for the germination and radical growth of crops. Low values of organic carbon, high humidity and fine textures are more susceptible. The appropriate values for the growth of any plant with these textures must not exceed 1.1 g cm<sup>−</sup><sup>3</sup> . Furthermore, a good structural stability helps keep particles together against different destabilizing forces that can act on a soil. Soil chemical condition like pH influences nutrient availability and soil microbial activity. In acid soils, few nutrients are available to be taken by the roots. Suitable values for horticultural crops are between 6 and 7.5 depending on the crop. The electrical conductivity determines the concentration of soluble salts present in the soil solution and can affect germination, plant growth or water absorption. Each crop has a different capacity to support soil salinity without

**121**

**Figure 2.**

*between treatments according to Tukey (p < 0.05) [33].*

*Soil Quality Problems Associated with Horticulture in the Southern Urban and Peri-Urban Area…*

experiencing detrimental effects on its development and production (tolerance). The organic carbon brings life to the soil, is a nutrient reserve, improves its physical conditions, improves soil structure and its porosity, increasing the aeration and water circulation that favors the development of the plant, regulates microbiological activities; privileges infiltration, decreasing soil erosion, improving soil water balance, tends to reduce evaporation and is a water reservoir. Well-supplied soils

The main degradations observed are edaphic salinization and alkalinisation, which are associated with waterlogging, development of pests and nutritional imbalances [13, 25–27]. These observations are partially coincident with those

Soils management and the use of groundwater for irrigation, do not often consider local properties, but are mainly based on information obtained in other parts of the world with characteristics very different from those described in the area of study. In general, there is a lack of knowledge and awareness of the processes involved in soil, air and water pollution. Producers from the southern green belt do not perform soil analysis prior to sowing or fertilizing, the quality of the irrigation water is unknown and soil management is performed based on the particular experience of each producer [1]. In many cases a "fertilization recipe" is applied without considering the physicochemical characteristics of the soil of each farm

Salts and sodium accumulation is exacerbated in soils with higher clay content since in these cases drainage is limited and therefore salts are not eluviated. Comparing 17 soil samples, obtained randomly from not cultivated sites (NC) placed within the horticultural farms (e.g., areas adjacent to the houses), in two districts from the southern green belt, it was found that soils from the district of La Plata (with higher clay content on the surface horizon) had higher electrical conductivity compared with soils from Florencio Varela (**Figure 2**). The crops present in the most of the sampled soils were chard, lettuce, onion, crucifixes and zukini. Likewise, salinization is also exacerbated in greenhouse cultivation systems with respect to open-field cultivation systems. In greenhouses, the excessive application of fertilizers, the use of low quality water with high content of sodium bicarbonate for irrigation, evapotranspiration that favors the accumulation of salts on the surface and the impossibility of washing with rainwater, further complicates the situation. Formerly, it was a common practice to remove the ceilings of the Greenhouses, made of glass, and allow the soil to be "washed" by the rain. Nowadays, this practice is less frequent, mainly because the cover of the greenhouses has been changed from

*Soil electrical conductivity in not cultivated soils per district. EC: electrical conductivity in water 1:2.5 by potentiometry [17]. Vertical bars indicate the standard deviation. Different letters show significant differences* 

reported for other regions of the country [28] and the world [29–31].

and without considering the nutrient demand of the crop [32].

*DOI: http://dx.doi.org/10.5772/intechopen.90351*

have carbon values between 4.5 and 6.5% [24].

### *Soil Quality Problems Associated with Horticulture in the Southern Urban and Peri-Urban Area… DOI: http://dx.doi.org/10.5772/intechopen.90351*

experiencing detrimental effects on its development and production (tolerance). The organic carbon brings life to the soil, is a nutrient reserve, improves its physical conditions, improves soil structure and its porosity, increasing the aeration and water circulation that favors the development of the plant, regulates microbiological activities; privileges infiltration, decreasing soil erosion, improving soil water balance, tends to reduce evaporation and is a water reservoir. Well-supplied soils have carbon values between 4.5 and 6.5% [24].

The main degradations observed are edaphic salinization and alkalinisation, which are associated with waterlogging, development of pests and nutritional imbalances [13, 25–27]. These observations are partially coincident with those reported for other regions of the country [28] and the world [29–31].

Soils management and the use of groundwater for irrigation, do not often consider local properties, but are mainly based on information obtained in other parts of the world with characteristics very different from those described in the area of study. In general, there is a lack of knowledge and awareness of the processes involved in soil, air and water pollution. Producers from the southern green belt do not perform soil analysis prior to sowing or fertilizing, the quality of the irrigation water is unknown and soil management is performed based on the particular experience of each producer [1]. In many cases a "fertilization recipe" is applied without considering the physicochemical characteristics of the soil of each farm and without considering the nutrient demand of the crop [32].

Salts and sodium accumulation is exacerbated in soils with higher clay content since in these cases drainage is limited and therefore salts are not eluviated. Comparing 17 soil samples, obtained randomly from not cultivated sites (NC) placed within the horticultural farms (e.g., areas adjacent to the houses), in two districts from the southern green belt, it was found that soils from the district of La Plata (with higher clay content on the surface horizon) had higher electrical conductivity compared with soils from Florencio Varela (**Figure 2**). The crops present in the most of the sampled soils were chard, lettuce, onion, crucifixes and zukini.

Likewise, salinization is also exacerbated in greenhouse cultivation systems with respect to open-field cultivation systems. In greenhouses, the excessive application of fertilizers, the use of low quality water with high content of sodium bicarbonate for irrigation, evapotranspiration that favors the accumulation of salts on the surface and the impossibility of washing with rainwater, further complicates the situation. Formerly, it was a common practice to remove the ceilings of the Greenhouses, made of glass, and allow the soil to be "washed" by the rain. Nowadays, this practice is less frequent, mainly because the cover of the greenhouses has been changed from

#### **Figure 2.**

*Urban Horticulture - Necessity of the Future*

high plasticity in B horizons.

reported 20.7 mg kg<sup>−</sup><sup>1</sup>

"pampean sediment" consisting of sand-clay silt with limestone (loess). However, the limestone is not present in the upper horizons due to washing. Properties as pH, organic matter and soluble salts make these soils suitable for agriculture. In addition, due to their topographic condition they are not affected by floods [9]. Most agricultural soils in the southern green belt belong to the Molisol and Vertisol orders [10] (Chernozems and Vertisols) [11]. They have a strong profile development with dark A horizons, generally thick and well provided with organic matter followed by B horizons enriched in eluviated clay accompanied, especially in Vertisols, by evidence of expansion and contraction of materials. These are soils with high cation exchange capacity given by both organic matter and clay content. From the physical point of view, high levels of clay and silt, makes them susceptible to changes in their physical properties. In some cases there is low permeability and

Low permeability is the main physical limitation for soils management in this area being more pronounced in the district of La Plata, where Vertisols with high clay content in surface (between 32 and 40%) and depth (50–60%), prevail. The

surroundings of La Plata reported levels of extractable P greater than 20 mg kg<sup>−</sup><sup>1</sup>

**3. Traditional horticulture in the southern Green belt of Buenos Aires**

Horticulture depends on the soil; therefore the conservation of this resource is essential to ensure the development of the sector. The intensive use of the soil, based on the overuse of inputs for many years (fertilizers, pesticides, disinfectants), added to irrigation with low quality water (sodium bicarbonate) [21], has generated negative impacts associated with soil pollution and degradation. The alteration of soil physical, chemical and biological properties resulted in a fragile productive

Soil physical condition establishes its sustainability, root penetration, air circula-

tion, water storage capacity, drainage, nutrient retention, among other factors. The texture (proportion clay, silt and sand) determine the amount and availability of water, nutrients, aeration and drainage. Soils with fine texture (clay more than 40% or silt more than 60%) have a high water and nutrient retention capacity. However, it must be handled with caution because they are easily compacted. Likewise, crops sensitive to soil pathogens are more susceptible in heavy textured soils. Fertirrigation has counteracted these disadvantages. Soil compaction reduces porosity and increases its bulk density. This limits the space for the storage or movement of air and water within the soil. It is the cause of a physical restriction for the germination and radical growth of crops. Low values of organic carbon, high humidity and fine textures are more susceptible. The appropriate values for the

a good structural stability helps keep particles together against different destabilizing forces that can act on a soil. Soil chemical condition like pH influences nutrient availability and soil microbial activity. In acid soils, few nutrients are available to be taken by the roots. Suitable values for horticultural crops are between 6 and 7.5 depending on the crop. The electrical conductivity determines the concentration of soluble salts present in the soil solution and can affect germination, plant growth or water absorption. Each crop has a different capacity to support soil salinity without

soils that were not under agriculture for at least the past 20 years. **Table 1** describes some physical and chemical properties of soils around the houses of horticultural

in soils from natural fields. Moreover, [13, 14] studying the

) [12]. However, [9]

. Furthermore,

in

only chemical limitation is low P content (less than 10 mg kg<sup>−</sup><sup>1</sup>

farmers from the southern green belt of Buenos Aires city.

system with a high risk of environmental impact [22, 23].

growth of any plant with these textures must not exceed 1.1 g cm<sup>−</sup><sup>3</sup>

**120**

*Soil electrical conductivity in not cultivated soils per district. EC: electrical conductivity in water 1:2.5 by potentiometry [17]. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according to Tukey (p < 0.05) [33].*

glass to plastic [13]. Thirteen soil samples were randomly obtained from horticultural farms from Florencio Varela district and it was observed that the electrical conductivity was higher in greenhouses than in open-field cultivation systems (**Figure 3**).

Although the electrical conductivity levels found in this study are still adequate for the growth of most horticultural species, some of them are at the limit. Vázquez and Terminiello (2008) found that saline concentrations greater than 1.2 ds m<sup>−</sup><sup>1</sup> affect the development and, consequently, the yield of onion, with a production reduction of 16% for every additional ds m<sup>−</sup><sup>1</sup> . Moreover, an adequate electrical conductivity should not exceed 1.5 ds m<sup>−</sup><sup>1</sup> for pepper [34] and 1.5 ds m<sup>−</sup><sup>1</sup> for tomato [35, 36]. [8] in a study carried out in greenhouses from La Plata district, found a high number of sites with high salinity levels with extremes that reached 10.6 ds m<sup>−</sup><sup>1</sup> . Under salinity conditions, there is a nutritional imbalance, due to different factors such as nutrient availability and competitive absorption.

Alkalization also represents an important problem in horticultural production. Cultivable soils from the southern peri-urban are naturally neutral or slightly alkaline but their alkalinity increases with horticultural use [9, 37]. Soils from the southern green belt were studied and it was observed that cultivated soils have higher pH, in both open-field and greenhouse cultivation systems, in comparison with non-cultivated soils.

It is important to consider that under high pH levels the availability of certain nutrients will be diminished, affecting crop development [38]. pH levels found in this study exceed the tolerance thresholds for many of the horticultural species grown in the southern green belt [39]. In this regard, [40] established that high pH levels (greater than 8) decrease the absorption of P and Ca+2 by crops, and on the contrary increase that of Mg+2, because the absorption of its competitive elements diminishes. Increases in pH and electrical conductivity in cultivated soils compared to uncultivated ones are mainly linked to the quality of the water used for irrigation. **Table 2** shows results from irrigation water analysis, sometimes also used for human consumption. The samples were taken from horticultural farms from the southern green belt of Buenos Aires. The results show that in addition to the low quality in terms of physicochemical characteristics, water samples have also microbiological contamination with faecal bacteria. This usually happens due to the high number of improperly drilled holes that cause leaks from nearby blind wells. Inadequate water management brings associated problems such as lower

#### **Figure 3.**

*Electrical conductivity values per system. EC: electrical conductivity in water 1:2.5 by potentiometry [17]; FC: open-fields cultivation systems; GC: greenhouses cultivation systems. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according to Tukey (p < 0.05). [33].*

**123**

*Soil Quality Problems Associated with Horticulture in the Southern Urban and Peri-Urban Area…*

**PA in 100 ml**

0 0 Maximum

0.10

 40 5.1 + 0 0.01 50 8.4 810 75 16.1 + 0 0.01 50 7.8 870 185 5.1 + 0 0.01 50 7.9 850 70 3 0 0 0.01 100 8.4 1240 30 16.1 0 + 0.01 25 8.1 730

**Count Investigation Nitrites Nitrates** pH **EC**

**ppm ppm μs cm<sup>−</sup><sup>1</sup>**

Maximum 45

6.5– 8.5

Maximum 400**\***

productivity, lower product quality, higher disease incidence, higher energy use and

alters the geometry of the pores, in turn affecting the permeability and retention of

was found in cultivated soils, both under open-field and greenhouse cultivation systems, compared with uncultivated soils from house surroundings. Samples were analysed using the Le Bissonnais [16] technique that assesses structural stability by calculating the mean weight diameter (MWD) of soils aggregate afte r being subjected to three pre-treatment conditions to determine the dispersive effect of different processes. Thus, T1 aims to show how dry soil behaves in the face of heavy rain, T2 how wet soil behaves in the face of intense rain and T3 how dry soil behaves in the face of mild rain and therefore a slow humidification. Uncultivated soils presented higher aggregate stability after every pre-treatment, with the average index (AVE I) of aggregate stability of 2.47 for uncultivated soils and 1.1 for cultivated soils (**Figure 4**). In addition, an increase in pH was observed in cultivated soils (**Figure 5**). **Table 3** shows the correlation found between aggregate stability and pH in soils

Studying soils from the southern green belt, a decrease in aggregate stability (AS)

In the same study, when bulk density was analysed, no significant differences were found between cultivated and uncultivated soils (**Figure 6**). This is probably linked to the fact that the sampling was performed after soil tillage was carried

causes expansion and/or dispersion of clays, which

High pH levels in the irrigation water are due to the fact that it has sodium bicarbonate. When irrigating with this water, the sodium cation is concentrated in the soil, generating an alkaline reaction. Another problem, not less important, associated with the presence of sodium (Na) in the soil is the effect that this cation has on soil structure. Soils with high exchangeable sodium content have dispersed colloids and therefore an unstable structure. Moreover, soil crusts are formed that seal the surface, creating or magnifying the problems of fluid exchange and impedance for plants (seedling emergence) and biological activity. The accumulation of

*MAB: mesophylls aerobic bacteria; TC: total coliforms; E. coli: Escherichia coli; PA: Pseudomonas aeruginosa; +, presence; 0, absence; pH: pH in water 1.2.5 and EC: electrical conductivity in water 1.2.5 by potentiometry [17].* 

lower efficiency in the use of water and fertilizers [42].

dispersing cations such as Na+

from the southern green belt.

water in the soil [38].

*DOI: http://dx.doi.org/10.5772/intechopen.90351*

**TC NMP 100 ml<sup>−</sup><sup>1</sup>**

Maximum 3

*References levels for drinking water quality according to CAA [41].*

*E coli* **in 100 ml**

**Well depth**

Drinking water quality

*\**

**Table 2.**

**m MAB**

**u.f.c. ml<sup>−</sup><sup>1</sup>**

Maximum 500

*of secondary importance according to CAA [41].*

*Irrigation water characteristics.*

*Soil Quality Problems Associated with Horticulture in the Southern Urban and Peri-Urban Area… DOI: http://dx.doi.org/10.5772/intechopen.90351*


*MAB: mesophylls aerobic bacteria; TC: total coliforms; E. coli: Escherichia coli; PA: Pseudomonas aeruginosa; +, presence; 0, absence; pH: pH in water 1.2.5 and EC: electrical conductivity in water 1.2.5 by potentiometry [17]. References levels for drinking water quality according to CAA [41]. \* of secondary importance according to CAA [41].*

#### **Table 2.**

*Urban Horticulture - Necessity of the Future*

reduction of 16% for every additional ds m<sup>−</sup><sup>1</sup>

cal conductivity should not exceed 1.5 ds m<sup>−</sup><sup>1</sup>

(**Figure 3**).

10.6 ds m<sup>−</sup><sup>1</sup>

with non-cultivated soils.

glass to plastic [13]. Thirteen soil samples were randomly obtained from horticultural farms from Florencio Varela district and it was observed that the electrical conductivity was higher in greenhouses than in open-field cultivation systems

tomato [35, 36]. [8] in a study carried out in greenhouses from La Plata district, found a high number of sites with high salinity levels with extremes that reached

Cultivable soils from the southern peri-urban are naturally neutral or slightly alkaline but their alkalinity increases with horticultural use [9, 37]. Soils from the southern green belt were studied and it was observed that cultivated soils have higher pH, in both open-field and greenhouse cultivation systems, in comparison

ferent factors such as nutrient availability and competitive absorption.

. Under salinity conditions, there is a nutritional imbalance, due to dif-

Alkalization also represents an important problem in horticultural production.

It is important to consider that under high pH levels the availability of certain nutrients will be diminished, affecting crop development [38]. pH levels found in this study exceed the tolerance thresholds for many of the horticultural species grown in the southern green belt [39]. In this regard, [40] established that high pH levels (greater than 8) decrease the absorption of P and Ca+2 by crops, and on the contrary increase that of Mg+2, because the absorption of its competitive elements diminishes. Increases in pH and electrical conductivity in cultivated soils compared to uncultivated ones are mainly linked to the quality of the water used for irrigation. **Table 2** shows results from irrigation water analysis, sometimes also used for human consumption. The samples were taken from horticultural farms from the southern green belt of Buenos Aires. The results show that in addition to the low quality in terms of physicochemical characteristics, water samples have also microbiological contamination with faecal bacteria. This usually happens due to the high number of improperly drilled holes that cause leaks from nearby blind wells. Inadequate water management brings associated problems such as lower

*Electrical conductivity values per system. EC: electrical conductivity in water 1:2.5 by potentiometry [17]; FC: open-fields cultivation systems; GC: greenhouses cultivation systems. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according to Tukey (p < 0.05). [33].*

Although the electrical conductivity levels found in this study are still adequate for the growth of most horticultural species, some of them are at the limit. Vázquez and Terminiello (2008) found that saline concentrations greater than 1.2 ds m<sup>−</sup><sup>1</sup> affect the development and, consequently, the yield of onion, with a production

. Moreover, an adequate electri-

for pepper [34] and 1.5 ds m<sup>−</sup><sup>1</sup>

for

**122**

**Figure 3.**

*Irrigation water characteristics.*

productivity, lower product quality, higher disease incidence, higher energy use and lower efficiency in the use of water and fertilizers [42].

High pH levels in the irrigation water are due to the fact that it has sodium bicarbonate. When irrigating with this water, the sodium cation is concentrated in the soil, generating an alkaline reaction. Another problem, not less important, associated with the presence of sodium (Na) in the soil is the effect that this cation has on soil structure. Soils with high exchangeable sodium content have dispersed colloids and therefore an unstable structure. Moreover, soil crusts are formed that seal the surface, creating or magnifying the problems of fluid exchange and impedance for plants (seedling emergence) and biological activity. The accumulation of dispersing cations such as Na<sup>+</sup> causes expansion and/or dispersion of clays, which alters the geometry of the pores, in turn affecting the permeability and retention of water in the soil [38].

Studying soils from the southern green belt, a decrease in aggregate stability (AS) was found in cultivated soils, both under open-field and greenhouse cultivation systems, compared with uncultivated soils from house surroundings. Samples were analysed using the Le Bissonnais [16] technique that assesses structural stability by calculating the mean weight diameter (MWD) of soils aggregate afte r being subjected to three pre-treatment conditions to determine the dispersive effect of different processes. Thus, T1 aims to show how dry soil behaves in the face of heavy rain, T2 how wet soil behaves in the face of intense rain and T3 how dry soil behaves in the face of mild rain and therefore a slow humidification. Uncultivated soils presented higher aggregate stability after every pre-treatment, with the average index (AVE I) of aggregate stability of 2.47 for uncultivated soils and 1.1 for cultivated soils (**Figure 4**).

In addition, an increase in pH was observed in cultivated soils (**Figure 5**). **Table 3** shows the correlation found between aggregate stability and pH in soils from the southern green belt.

In the same study, when bulk density was analysed, no significant differences were found between cultivated and uncultivated soils (**Figure 6**). This is probably linked to the fact that the sampling was performed after soil tillage was carried

#### **Figure 4.**

*Aggregate stability by Le Bissonnais method [16]. MWD: mean weight diameter; C: cultivation sites; NC: not cultivated; T1: dry soil behavior in the face of heavy rain; T2: wet soil behavior in the face of heavy rain; T3: dry soil behavior in the face of mild rain; AVE I: average index of the three pretreatments. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according to Tukey (p < 0.05) [33].*

#### **Figure 5.**

*Soils pH values. pH: pH in water 1: 2.5 by potentiometry [17]; C: cultivation; NC: not cultivated sites. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according to Tukey (p < 0.05) [33].*


*T1: dry soil behavior in the face of heavy rain; T2: wet soil behavior in the face of heavy rain; T3: dry soil behavior in the face of mild rain; AVE I: average index of the three pre-treatments [16]; pH: pH in water 1.2.5 by potentiometry [16]. Significant correlations are presented with p < 0.05 [32].*

#### **Table 3.**

*Pearson correlation coefficients (r) between pH and aggregate stability treatments.*

out in cultivated soils. Soil crusting and compaction due to structural instability leave producers with no options but to increase pre-sowing tillage to ensure crops emergence and growth. This causes greater aggregates destruction and formation

**125**

**Figure 6.**

*according to Tukey (p < 0.05) [33].*

*Soil Quality Problems Associated with Horticulture in the Southern Urban and Peri-Urban Area…*

) leading to nutritional imbalances and

. It is also observed that the

of a plow floor that require re-tillage the soil generating a vicious circle that also increases production costs due to the high fuel use required for tillage tasks. This instability of the production system causes, a few years after the start of production, the decrease in crop yields due to land degradation linked to the interconnection of the following problems: salinization, alkalization, decreased permeability, flooding, nutritional imbalances and development of diseases. To counteract the negative effects crop yields and without performing the appropriate analysis, fertilization doses are increased, adding soil hyperfertilization to the aforementioned problems [26] and increasing costs of production and environmental damage [37, 43]. It is common to try to reverse the decrease in yield by increasing the addition of fertilizers and phosphoric acid. Occasionally, there is a favorable initial response of the crop to greater fertilization, generating the wrong idea that it effectively contributes to improving the productive environment. However, eventually over fertilization occurs, and the problems associated with land degradation are exacerbated [21, 43] since these practices do not alleviate pH imbalances in a sustained manner and, on the contrary, they generate a negative effect due to the excessive

contamination [14, 43, 44]. With such high concentrations of P in the soil there is no response to fertilization [45] in addition, the availability of P not only depends on chemical fertilization, but also on the response or interaction with Ca+2, Mg+2, Al+3, Fe+3 and Mn+2 [46]. Thus, in high pH situations, P forms insoluble compounds

**Figure 7** shows extractable P levels by Bray and Kurtz 1 found horticultural farms from the southern peri-urban. Sampling sites included soils under open-field and greenhouse cultivation systems and uncultivated soils adjacent to the houses. The range of extractable P concentrations varied from 50.7 to extremely high levels

minimum levels obtained from cultivated sites double the maximum level from uncultivated sites. It is also interesting to note that the levels found in uncultivated sites are well above what soils should have in their natural state [9, 12, 34], so it could be hypothesized that such high P contents, would exceed soils retention capacity, therefore remaining in solution and being able to reach uncultivated sites from adjacent cultivated areas. In this sense, [48] reported contamination of a river basin in the southern peri-urban area with P derived from the horticultural activity.

*Bulk density values. BD: bulk density by cylinder method [15]; C: cultivation sites; NC: not cultivated. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments* 

with Ca+2 and Mg+2 [45], leading to induced deficiencies. This has also been reported in other parts of the world with negative consequences on the environ-

, with an average of 255.0 mg kg<sup>−</sup><sup>1</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.90351*

accumulation of P (greater than 300 mg kg<sup>−</sup><sup>1</sup>

ment, production and economics [47].

as 538.7 mg kg<sup>−</sup><sup>1</sup>

### *Soil Quality Problems Associated with Horticulture in the Southern Urban and Peri-Urban Area… DOI: http://dx.doi.org/10.5772/intechopen.90351*

of a plow floor that require re-tillage the soil generating a vicious circle that also increases production costs due to the high fuel use required for tillage tasks.

This instability of the production system causes, a few years after the start of production, the decrease in crop yields due to land degradation linked to the interconnection of the following problems: salinization, alkalization, decreased permeability, flooding, nutritional imbalances and development of diseases. To counteract the negative effects crop yields and without performing the appropriate analysis, fertilization doses are increased, adding soil hyperfertilization to the aforementioned problems [26] and increasing costs of production and environmental damage [37, 43].

It is common to try to reverse the decrease in yield by increasing the addition of fertilizers and phosphoric acid. Occasionally, there is a favorable initial response of the crop to greater fertilization, generating the wrong idea that it effectively contributes to improving the productive environment. However, eventually over fertilization occurs, and the problems associated with land degradation are exacerbated [21, 43] since these practices do not alleviate pH imbalances in a sustained manner and, on the contrary, they generate a negative effect due to the excessive accumulation of P (greater than 300 mg kg<sup>−</sup><sup>1</sup> ) leading to nutritional imbalances and contamination [14, 43, 44]. With such high concentrations of P in the soil there is no response to fertilization [45] in addition, the availability of P not only depends on chemical fertilization, but also on the response or interaction with Ca+2, Mg+2, Al+3, Fe+3 and Mn+2 [46]. Thus, in high pH situations, P forms insoluble compounds with Ca+2 and Mg+2 [45], leading to induced deficiencies. This has also been reported in other parts of the world with negative consequences on the environment, production and economics [47].

**Figure 7** shows extractable P levels by Bray and Kurtz 1 found horticultural farms from the southern peri-urban. Sampling sites included soils under open-field and greenhouse cultivation systems and uncultivated soils adjacent to the houses. The range of extractable P concentrations varied from 50.7 to extremely high levels as 538.7 mg kg<sup>−</sup><sup>1</sup> , with an average of 255.0 mg kg<sup>−</sup><sup>1</sup> . It is also observed that the minimum levels obtained from cultivated sites double the maximum level from uncultivated sites. It is also interesting to note that the levels found in uncultivated sites are well above what soils should have in their natural state [9, 12, 34], so it could be hypothesized that such high P contents, would exceed soils retention capacity, therefore remaining in solution and being able to reach uncultivated sites from adjacent cultivated areas. In this sense, [48] reported contamination of a river basin in the southern peri-urban area with P derived from the horticultural activity.

#### **Figure 6.**

*Urban Horticulture - Necessity of the Future*

**124**

**Table 3.**

**Figure 5.**

*to Tukey (p < 0.05) [33].*

**Figure 4.**

*(p < 0.05) [33].*

T1 **1**

T2 0.66 **1**

*[16]. Significant correlations are presented with p < 0.05 [32].*

T3 0.91 0.73 **1**

*Pearson correlation coefficients (r) between pH and aggregate stability treatments.*

AVE I 0.95 0.79 0.97 **1**

out in cultivated soils. Soil crusting and compaction due to structural instability leave producers with no options but to increase pre-sowing tillage to ensure crops emergence and growth. This causes greater aggregates destruction and formation

pH −0.75 −0.44 −0.7 −0.7 **1** *T1: dry soil behavior in the face of heavy rain; T2: wet soil behavior in the face of heavy rain; T3: dry soil behavior in the face of mild rain; AVE I: average index of the three pre-treatments [16]; pH: pH in water 1.2.5 by potentiometry* 

*Soils pH values. pH: pH in water 1: 2.5 by potentiometry [17]; C: cultivation; NC: not cultivated sites. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according* 

*Aggregate stability by Le Bissonnais method [16]. MWD: mean weight diameter; C: cultivation sites; NC: not cultivated; T1: dry soil behavior in the face of heavy rain; T2: wet soil behavior in the face of heavy rain; T3: dry soil behavior in the face of mild rain; AVE I: average index of the three pretreatments. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according to Tukey* 

**T1 T2 T3 AVE I pH**

*Bulk density values. BD: bulk density by cylinder method [15]; C: cultivation sites; NC: not cultivated. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according to Tukey (p < 0.05) [33].*

**Figure 7.**

*Extractable phosphorus values in C: cultivated and NC: not cultivated sites. EP: extractable phosphorus by Bray and Kurtz 1 [20].*

At present, there are few works that analyse the changes in the P content of the soil due to horticulture or that explain the causes of such accumulations of P in uncultivated sites in the area.

Another horticultural practice proposed as a possible solution to degradation soil but ended up generating major problems, is the use of poultry litter as organic fertilizer. This organic amendment is widely used in the area to improve the organic matter content of the soil and thus improve its structure; however, its excessive application is a potential source of soil and water contamination. In addition to providing nutrients, these fertilizers introduce salts and pollutants into the soil and, in general, these poultry litters are characterized by having high pH, high electrical conductivity and high P content, which contribute to worsen the aforementioned problems. These materials are very variable in their composition and therefore should be analysed prior to soil application. As an example, when analysing a poultry litter sample from a supplier from the area under study, pH levels found were between 7.6 and 8.6; electrical conductivity values between 3 and 7.8 dS m<sup>−</sup><sup>1</sup> , TOC between 34 and 45%, total N content between 2.08 and 2.42% and the C/N ratio between 16.3 and 18.6%. The extractable P content found ranged between 1600 and 3900 mg kg<sup>−</sup><sup>1</sup> and total P between 6500 and 12,000 mg kg<sup>−</sup><sup>1</sup> . Other authors have reported average total P content of 8700 mg kg<sup>−</sup><sup>1</sup> [25], although concentrations higher than 10,000 mg kg<sup>−</sup><sup>1</sup> have been detected in poultry litter and poultry manure [49, 50]. These characteristics depend on the composting time and the climatic conditions during composting. A poultry litter supplier usually sells to several horticultural farms of the area.

However, beyond all the negative characteristics of the poultry litter, some authors have proposed the use of these organic amendments as a promising practice to improve or mitigate the impact of horticultural production on the soil [51, 52]. An important process that is undergone in the horticultural soils under study is the progressive loss of organic matter [53]. [54] argue about the advantages of poultry residues and underline that they not only contribute with significant amounts of nutrients but also organic matter, which has a favorable effect on soils structure and permeability which is usually limited in the green belt area. However, other authors claim that the addition of poultry litter does not lead to significant increases in total oxidative carbon (TOC), since organic humus-forming materials are those of plant origin [26, 55]. The labile fractions of organic matter, such as those represented by the particulate oxidative carbon (POC), are much more sensitive to changes in management practices. Therefore, when a change in practices is made, the dynamics of these fractions are altered, affecting the physical, chemical and biochemical

**127**

*Soil Quality Problems Associated with Horticulture in the Southern Urban and Peri-Urban Area…*

environment of the soil [56]. Oxidative carbon associated with the mineral fraction (MOC) corresponds to a more complex and stable humus, which requires more time for its formation, making it difficult to increase its content through agricul-

*Organic carbon fractions. TOC: total oxidative carbon by Walkley and Black [18]; MOC: oxidative carbon associated with the mineral fraction and POC: particulate oxidative carbon [19]. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according to Tukey (p < 0.05) [33].*

**Figure 8** shows the results obtained from soils sampled in horticultural farms from the districts of La Plata and Florencio Varela where poultry litter is applied regularly every year, in some cases on more than one occasion. In the present study, the contents of TOC and MOC were lower in cultivated sites than in uncultivated sites. In addition, it should be noted that the POC was also lower in cultivated sites, indicating that the addition of poultry litter is not enough to counteract the loss of organic carbon associated with horticulture, not even those fractions of rapid

In the last years and in different parts of the world, the way the city is inhabited

Food production within the city is mainly used for self-consumption, to improve the amount of available food, for its freshness, variety and nutritional value [61], for environmental education and the exchange of experiences, among other factors, as [62] points out. It is also associated with jobs generation and income for groups of individuals, and it promotes environmental sanitation through the recycling of organic waste [63]. As it is a multifunctional and multicomponent activity, urban agriculture can respond to a great diversity of urban issues that include from the fight against poverty and the strengthening of self-esteem, to the improvement of

has been transformed; the daily relationship between human beings and their natural environment within the city has changed [58]. During the twentieth century, urban agriculture reached a great development due to increasing urbanization, deterioration of life conditions in poor neighborhoods, wars, natural disasters, environmental degradation and lack of resources, which caused food shortage. Urban agriculture means food production within the cities, in most cases it is a small-scale activity scattered throughout the city [59]. The large number of community horticultural gardens located in charitable dining rooms and in vacant spaces (for example, under high-voltage lines or along roads and waterways), or in institutional spaces such as hospitals and businesses, family gardens in backyards and roofs and school gardens are just a few examples that show the growing presence of

*DOI: http://dx.doi.org/10.5772/intechopen.90351*

tural practices in the short term.

**Figure 8.**

**4. Horticulture in the city**

agriculture in the cities [60].

cycling. Similar results were found by [8, 57].

*Soil Quality Problems Associated with Horticulture in the Southern Urban and Peri-Urban Area… DOI: http://dx.doi.org/10.5772/intechopen.90351*

**Figure 8.**

*Urban Horticulture - Necessity of the Future*

vated sites in the area.

*Bray and Kurtz 1 [20].*

**Figure 7.**

At present, there are few works that analyse the changes in the P content of the soil due to horticulture or that explain the causes of such accumulations of P in unculti-

*Extractable phosphorus values in C: cultivated and NC: not cultivated sites. EP: extractable phosphorus by* 

Another horticultural practice proposed as a possible solution to degradation soil but ended up generating major problems, is the use of poultry litter as organic fertilizer. This organic amendment is widely used in the area to improve the organic matter content of the soil and thus improve its structure; however, its excessive application is a potential source of soil and water contamination. In addition to providing nutrients, these fertilizers introduce salts and pollutants into the soil and, in general, these poultry litters are characterized by having high pH, high electrical conductivity and high P content, which contribute to worsen the aforementioned problems. These materials are very variable in their composition and therefore should be analysed prior to soil application. As an example, when analysing a poultry litter sample from a supplier from the area under study, pH levels found were between 7.6 and 8.6;

total N content between 2.08 and 2.42% and the C/N ratio between 16.3 and 18.6%.

have been detected in poultry litter and poultry manure [49, 50]. These characteristics depend on the composting time and the climatic conditions during composting. A poultry litter supplier usually sells to several horticultural farms of the area. However, beyond all the negative characteristics of the poultry litter, some authors have proposed the use of these organic amendments as a promising practice to improve or mitigate the impact of horticultural production on the soil [51, 52]. An important process that is undergone in the horticultural soils under study is the progressive loss of organic matter [53]. [54] argue about the advantages of poultry residues and underline that they not only contribute with significant amounts of nutrients but also organic matter, which has a favorable effect on soils structure and permeability which is usually limited in the green belt area. However, other authors claim that the addition of poultry litter does not lead to significant increases in total oxidative carbon (TOC), since organic humus-forming materials are those of plant origin [26, 55]. The labile fractions of organic matter, such as those represented by the particulate oxidative carbon (POC), are much more sensitive to changes in management practices. Therefore, when a change in practices is made, the dynamics of these fractions are altered, affecting the physical, chemical and biochemical

The extractable P content found ranged between 1600 and 3900 mg kg<sup>−</sup><sup>1</sup>

, TOC between 34 and 45%,

. Other authors have reported average total P

[25], although concentrations higher than 10,000 mg kg<sup>−</sup><sup>1</sup>

and total

electrical conductivity values between 3 and 7.8 dS m<sup>−</sup><sup>1</sup>

P between 6500 and 12,000 mg kg<sup>−</sup><sup>1</sup>

content of 8700 mg kg<sup>−</sup><sup>1</sup>

**126**

*Organic carbon fractions. TOC: total oxidative carbon by Walkley and Black [18]; MOC: oxidative carbon associated with the mineral fraction and POC: particulate oxidative carbon [19]. Vertical bars indicate the standard deviation. Different letters show significant differences between treatments according to Tukey (p < 0.05) [33].*

environment of the soil [56]. Oxidative carbon associated with the mineral fraction (MOC) corresponds to a more complex and stable humus, which requires more time for its formation, making it difficult to increase its content through agricultural practices in the short term.

**Figure 8** shows the results obtained from soils sampled in horticultural farms from the districts of La Plata and Florencio Varela where poultry litter is applied regularly every year, in some cases on more than one occasion. In the present study, the contents of TOC and MOC were lower in cultivated sites than in uncultivated sites. In addition, it should be noted that the POC was also lower in cultivated sites, indicating that the addition of poultry litter is not enough to counteract the loss of organic carbon associated with horticulture, not even those fractions of rapid cycling. Similar results were found by [8, 57].
